E. Cattan

Structure control of Pb(Zr,Ti)O3 films using PbTiO3 buffer layers produced by magnetron sputtering

The orientation of Pb(Zr,Ti)O3 (PZT) thin films grown by sputtering on a Si/SiO2/Ti/Pt substrate using a PbTiO3 (PT) buffer layer was controlled by changing the thickness of the buffer layer. The x-ray diffraction of PT as a function of the thickness, in the range of 20–400 A, showed modification of the PT orientation. That suggests a gradual evolution of the lattice parameters in the nucleation stage of PT films. The main growth mechanism was certainly due to the passing from an island growth to a continuous layer. The (111) oriented and (100) oriented PZT films were grown on 50 and 200 A PT buffer layers, respectively.

Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution

Ion beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) with x equal to 0.54 thin films grown on Pt/Ti/SiO2/Si substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters (current density, acceleration voltage, gas pressure) has been investigated. The PZT etch rate can reach 600 A/min with acceleration voltage of 1000 V and current density of 1 mA/cm2. Selectivity ratios between PZT and masks of various natures (photoresist, Pt, Ti) have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out C(V) and hysteresis loops P(E) measurements before and after etching have provided evidence of degradation. We noted a l...

True Young modulus of Pb(Zr,Ti)O3 films measured by nanoindentation

In order to assess transverse elastic modulus of lead zirconate titanate (PZT) thin films, we used a nanoindenter with constant monitoring of the force. It is shown that the true elastic modulus, i.e., the low pressure elastic modulus, can be measured by this method. This permitted a determination that sputter deposited PZT (54∕46) films display a Young modulus close to a ferroelectric hard type PZT bulk ceramic. Moreover, this low pressure modulus is independent of grain size and thickness of the film, but this is no more true for high pressure modulus. This provides a step toward a better understanding of the properties of these PZT films and the possibility to better use them in microsystems.

Evaluation of niobium effects on the longitudinal piezoelectric coefficients of Pb(Zr, Ti)O3 thin films

Pb(Zr, Ti)O-3 (PZT) and Pb(Zr, Ti, Nb)O-3 (PNZT) thin films have been deposited on platinized silicon substrates by sputtering followed by a postannealing treatment. The Nb concentration in the films varied between 1 and 7 at. % with increments of 1 at. %. The effects of Nb modification on the piezoelectric response, and particularly on the longitudinal piezoelectric coefficient d(33), have been investigated. The introduction of Nb enhances the dielectric and piezoelectric properties of the PZT films. The best doping level ranges from 1 up to 2 at. %. The relative dielectric constant epsilon(r), reaches 1100, and the maximum value of d(33) is equal to 115 pm/V for a 1 at. % Nb-doped PZT in comparison to 820 and 55 pm/V for an undoped PZT film. PNZT films are suitable for microsystem applications

e31 piezoelectric constant measurement of lead zirconate titanate thin films

The piezoelectric constant e31 measurement procedure is presented for sputtered lead zirconate titanate (PZT) thin films deposited on silicon substrates. With a simple cantilever used in the direct piezoelectric effect, it is possible to measure piezoelectric coefficients of unpoled and poled films. We discuss the poling treatment effects; applied electric field amplitude and duration on the piezoelectric response. We have registered a quasistatic piezoelectric hysteresis loop, and will show that the poling procedure can modify the symmetry of the hysteresis loop. The thin films were piezoelectric in a virgin state, which causes the offset of the piezoelectric hysteresis loops. The maximum remanent piezoelectric constant e31 estimated for sputtered PZT thin film is −4 C/m2.

Determination of the d31 piezoelectric coefficient of PbZrxTi1−xO3 thin films using multilayer buckled micromembranes

The aim of this paper consists in the determination of the piezoelectric transverse coefficient d31 of PbZrxTi1−xO3 (PZT) thin films integrated in dedicated multilayer silicon-based micromembranes exhibiting an initial buckled profile. An analytical model specific to this configuration was built and used for the calculation of d31 starting with the static profiles of the microfabricated devices determined by means of a double-beam interferometer. The influence of dc voltage and buckling effects on the d31 piezoelectric coefficient at the microscale were investigated, and high values were obtained, from 30to75pm∕V, within a hysteresyslike cycle. These results demonstrated the good electrical behavior of PZT thin films at the microscale with a low influence of buckling effects and determined optimal operation conditions for high values of d31.

Micromachining SU-8 pivot structures using AZ photoresist as direct sacrificial layers for a large wing displacement

This paper presents the micromachining of SU-8 pivot structures. A new processing method was proposed using AZ 4562 as sacrificial layers to create a controlled air gap in the pivot region. These three-dimensional SU-8 pivot structures are designed to obtain a large wing displacement of the bio-mimetic flying micromachine. Several sacrificial methods used for the fabrication of SU-8 structures were reviewed and compared. A new process featuring AZ 4562 sacrificial layers was developed. Two relevant effects, the scission and outgassing effects, were greatly weakened to acquire a better SU-8/AZ interface. It was found that AZ 4562 could be directly deposited on SU-8 without any barrier layer between AZ 4562 and SU-8. So, AZ 4562 can be used directly as a thick sacrificial layer, thus greatly simplifying the fabrication process. SU-8 reinforcing patches can be added to compensate for the loss in the thickness of the central beam in the pivot regions. Using this new method, SU-8 pivot structures with different central beams, either straight or L-shaped, were successfully materialized. The air gap obtained was large and reached ~100 µm, thus helping to produce a large wing displacement. The fabrication precision and its main factors were evaluated. The deviation of actual structure size from design value was 2–7%, depending on the material and technique involved. Preliminary measurements of the fabricated structure indicating that a large wing displacement, flexure angle and torsion angle can be achieved. This new process is simple, low cost and compatible with standard MEMS technology.

Electrical damage induced by reactive ion-beam etching of lead-zirconate-titanate thin films

Ion-beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) thin films with x equal to 0.54 grown on Pt∕TiOx∕SiO2∕Si substrates has been performed using pure Ar gas and a varying CHF3∕Ar gas mixing ratio. The etch rate dependence on the process parameters (gas composition, current density, and acceleration voltage) has been investigated. PZT etch rate under 40% CHF3 in Ar can reach 100nm∕min with an acceleration voltage of 900 V and a current density of 0.7mA∕cm2 (in comparison to 35nm∕min in pure Ar). A selectivity ratio of 8 has been obtained between PZT and photoresist (1.3 in pure Ar). We have evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases less under a gas mixture than under a pure argon beam, and that the preferential etching observed at the grain boundaries under a pure argon beam disappears when we increase the proportion of CHF3 in the gas mixture. For some etching parameters (current density, acceleration voltage, and gas mixing ratio), w...

PZT thin film Bi-layer devices for phase controlled actuation in MEMS

A potential application for ferroelectric thin films is micro positioning and actuation. For using PZT films as micro-actuators it is desirable to have film thicknesses of comparable size to the underlying structure. The amount of actuation possible is determined by a number of factors: the piezoelectric coefficient d31, geometric factors and the compliance of both the actuator and cantilever and the electric field across the film. Using a bi-layer should therefore increase the amount of actuation for a given drive voltage. Bi-layer devices can also be driven at constant voltage, and their actuation varied by the phase difference of the drive voltage between the two layers. PZT films of thickness 0.5 μm have been deposited as a bi-layer. Micro-actuators have been fabricated using these structures, their electric properties measured and their electro-mechanical properties characterised and evaluated using optical beam deflection.

Top-down Approach for the Direct Synthesis, Patterning, and Operation of Artificial Micromuscles on Flexible Substrates

Recent progress in the field of microsystems on flexible substrates raises the need for alternatives to the stiffness of classical actuation technologies. This paper reports a top-down process to microfabricate soft conducting polymer actuators on substrates on which they ultimately operate. The bending microactuators were fabricated by sequentially stacking layers using a layer polymerization by layer polymerization of conducting polymer electrodes and a solid polymer electrolyte. Standalone microbeams thinner than 10 μm were fabricated on SU-8 substrates associated with a bottom gold electrical contact. The operation of microactuators was demonstrated in air and at low voltage (±4 V).